1. Field of the Invention
The present invention relates to apparatus having the function of forming an image on paper which is fed initially and thereafter forming another image on the same paper which is fed again.
2. Description of the Related Art
Copying machines are already provided which have the function of forming an image on paper fed from a feed outlet (i.e., an outlet for feeding paper having no image formed thereon, hereinafter referred to as the "initial feed outlet") of the main unit, thereafter temporarily holding the paper as accommodated in an intermediate containing portion and subsequently feeding the paper again from a refeed outlet (i.e., a feed outlet of the intermediate containing portion) to thereby form another image on the same paper (duplex copying function or composite copying function).
Also provided are copying machines equipped with an automatic document feeder (ADF).
Copying machines are further available which have such a function that when the absence of paper in a paper tray is detected during feeding, the feed outlet is changed over from the tray to another paper tray containing paper of the same-size to continue the feeding operation.
Further available are copying machines having the duplex copying function and so adapted that upon the detection of feeding of a specified number of paper sheets from the initial feed outlet in the main unit for first face copying, a command is given to refeed the paper from the refeed outlet of the intermediate containing portion so as to shorten the waiting time before the start of second face copying.
With image forming apparatus having the function of repeatedly forming an image on the same paper like the duplex copying function, it is desired to improve the productivity of prints, so that it is required to feed paper sheets at shortened intervals as a method of achieving the improvement.
The paper feeding intervals to be shortened include not only the interval between the specified number of paper sheets but also the interval after the completion of initial feeding of the specified number of sheets for first face printing and until the initiation of refeeding for second face printing, and the interval after the completion of refeeding for the second face printing and until the initiation of the next initial feeding for the first face printing.
However, if an attempt is made to merely shorten the interval until the initiation of refeeding for the second face printing and the interval until the initiation of the next initial feeding for the first face printing without giving consideration, for example, to the specified number of prints to be made or to the length of path of transport, there is the likelihood of a collision occurring between the initially fed paper and the refed paper at a junction of the transport path from the initial feeding side and the transport path from the refeeding side, giving rise to a transport trouble.
Discrimination data indicating the feed source (initial feed outlet/refeed outlet) is given to each sheet of paper to make distinction as to whether the printed sheet is to be discharged from the machine or to be accommodated in the tray of the intermediate containing portion. Suppose jam troubles occurring are corrected based on the discrimination data. When a jam occurred before a fifth sheet P5 having images of documents D1, D2 printed on the respective front and rear faces thereof is discharged from the machine as shown in FIG. 19 (the specified number of prints in the illustrated case: 5), the jam is corrected based on the interpretation that the documents D1, D2 have not been copied. More specifically, a command is given to the effect that the documents D1, D2 are to be returned to a document tray 31. Accordingly, in the case where a sheet bearing a print of document D3 on its first face remains in the tray 25 of the intermediate containing portion as illustrated, the system as it is permits occurrence of the trouble that an image of document D1 is printed on the second face of the sheet.